The present invention relates to spiral-type kneading machines for industrial use for preparing flour-based mixtures. In particular, the invention relates to the field of so-called xe2x80x9cspiral-typexe2x80x9d kneading machines, i.e. of the type comprising a supporting structure, a bowl carried by the supporting structure, and spiral-shaped rotating mixing means arranged within the bowl.
According to the conventional art, the bowl for the preparation of the mixture has a circular shape and is driven in rotation around its axis. The kneading means consist of a spiral shaped tool which protrudes downwards inside the bowl starting from an auxiliary supporting structure which projects in a cantilever fashion above the bowl. The spiral-shaped tool is driven in rotation about an axis spaced apart from the axis of the bowl and has an overall volume which therefore occupies only a portion of the space contained inside the bowl. The rotation of the bowl has precisely the purpose of bringing the various portions of the product contained in the bowl into the area occupied by the mixing tool. In addition, precisely because the spiral-shaped tool occupies an eccentric part of the space inside the bowl, in these known machines there is at times present a central column either protruding from the bottom of the bowl or descending from a head that surmounts the bowl, in order to delimit, on the side facing towards the center of the bowl, the space swept by the mixing tool, and thus to favour better working of the mixture between the tool and the wall of the bowl.
The machines of the above described type have undergone various developments. The applicant has devised and developed various improvements (see for example the European Patents EP-B-0 354 190, EP-B-0 551 571 and EP-B-0 714 606), such as the use of two or more spiral-shaped tools or the solution of a machine operating in a continuous way to produce a continuous flow of mixed product. Naturally, all the above mentioned improvements increase the productivity of the machine and the quality of the product on one hand, but on the other hand they imply more or less burdensome complications in the structure of the machine itself, and consequently entail an increase in machine cost.
A kneading machine for laboratories is also known (see U.S. Pat. No. 5,906,432), which can be used to test mixtures, comprising a non-rotating bowl, kneading means arranged within the bowl, comprising at least one spiral-shaped tool, consisting of a substantially helical arm lying between two theoretical co-axial cylindrical surfaces, which are tangent to this helical arm on the outer and inner side thereof, and a fixed member for engaging the mixture, projecting from the bottom of the bowl.
However, in the case of this known machine, the axis of the kneading tool is always out of centre with respect to the bowl, as in the above described conventional machines, and the tool has a theoretical cylinder which occupies only a portion of the space within the bowl. Furthermore, since the bowl does not rotate, in this case the axis of the kneading tool is driven through a planetary path around the bowl axis, in order to engage the entire product contained within the bowl. The solution implies a relatively complicated structure of the machine and does not allow in any case for a very reduced kneading time. Furthermore, the fixed member provided in this machine is arranged at the centre of the bowl.
From document EP-A-0 000 512, a mixing device is also known for powder-like bulk solids comprising a non-rotating container and a stirring tool with a rotating auger at the center of the container occupying the entire inner space of the container. Devices of this type belong to a class of products which is out of the field of the invention, since they make use of auger-type stirrers which have only the function to displace the solid particles inside the container and could not provide a kneading action in any way. Furthermore, in this known device a fixed member co-operating with the rotating member is absent, since no kneading action is requested therein.
The object of the present invention is that of providing a spiral-type kneading machine for industrial use, for the preparation of flour-based mixtures, which has an extremely simple structure and at the same time is able to substantially shorten the time necessary for obtaining a dough of the desired quality.
In view of achieving this object, the present invention provides a kneading machine comprising:
a non-rotating bowl,
kneading means arranged within the bowl, comprising at least a spiral-shaped tool consisting of a substantially helical arm lying between two theoretical coaxial cylindrical surfaces which are tangent to the helical arm on the outer and inner side thereof, and
a fixed member for engaging the mixed dough projecting from the bottom of the bowl,
characterised in that:
said spiral-type kneading tool has its axis substantially coincident with the axis of the bowl and occupies substantially the entire apace contained within the bowl,
said fixed member projecting from the bottom of the bowl is spaced from the central axis of the bowl, so as to engage the product being mixed, preventing the formation at the centre of the bowl of a mass of product which could tend to be driven in rotation around itself by the kneading tool, without being mixed.
In a preferred embodiment of the invention, the above mentioned fixed member is in form of a finger projecting upwardly from the bottom of the bowl and having a curved portion which is substantially tangent to the theoretical inner cylindrical surface of the spiral-shaped tool, so as to cooperate with the kneading tool in the kneading action. Preferably, the circular bowl has a planar bottom wall and a cylindrical wall having a lower portion with a rounded profile connected to the bottom wall. In this case, also preferably, the kneading tool has a lower end portion which extends adjacent to said lower portion with rounded profile of the bowl and projects radially inwardly from said theoretical cylindrical surface of the tool. In this manner, the formation of a mass of non-mixed product at the center of the bowl is further prevented. As a consequence of this arrangement, the fixed member has a base located on the bottom of the bowl at a distance from the axis of the bowl which is lower than that of the lower end of the kneading tool, and a main portion located at a greater distance. Preferably, the fixed member is constituted by a finger with a circular cross section and the above mentioned main portion thereof extends substantially in a radial plane relative to the bowl and has a curved shape, with a concavity facing towards the axis of the bowl, so that said fixed member has an overall shape in form of a sickle. Studies and tests of the applicant have shown that this shape gives particular advantages with regard to the co-operation between the fixed member and the kneading tool during the kneading action, so that the kneading time is decreased, while the fixed member fulfils its function of preventing formation of a non-mixed mass of product. It is believed that this more efficient kneading action is due to that the spiral-shaped tool presses the dough to be mixed by making it to pass forcibly through a narrow passage between the wall of the circular bowl and the above mentioned curved portion of the fixed member.
Also in the case of the preferred embodiment, the bottom of the wall has a removable portion for discharge of the mixed product at the end of the kneading cycle. However, a solution is not excluded which makes use of an auxiliary supporting structure for the spiral-shaped tool which is vertically movable between a lowered operative position and a raised operative position, in which the spiral-shaped kneading means come out of the bowl so that the latter may be moved away in order to be emptied.
According to a further preferred feature of the invention, the spiral-shaped tool has a scraper in sliding contact with the inner surface of the bowl, preferably constituted by a spatula made of a material having a low coefficient of friction.